This relates generally to imaging devices, and more particularly, to imaging devices with trench isolated circuitry.
Modern electronic devices such a cellular telephones, cameras, and computers often use digital image sensors. Imagers (i.e., image sensors) may be formed from a two-dimensional array of image sensing pixels. Each pixel may include a photosensor such as a photodiode that receives incident photons (light) and converts the photons into electrical signals. Conventional image pixel arrays include frontside illuminated image pixels or backside illuminated image pixels. Image pixels are fabricated on a semiconductor substrate using complementary metal-oxide-semiconductor (CMOS) technology or charge-coupled device (CCD) technology. The image sensors may include photodiodes and other operational circuitry such as transistors formed in a front surface of the substrate. In an image sensor having frontside illuminated image pixels, a dielectric stack is formed on the front surface of the substrate directly on top of the photodiodes. The dielectric stack includes metal routing lines and metal vias formed in dielectric material. Image light passes through the dielectric stack to the photodiodes. In an image sensor having backside illuminated image pixels, the photodiodes are formed on a thinned semiconductor substrate and receive image light through the backside of the semiconductor substrate so that the light does not pass through the dielectric stack.
Both frontside and backside illuminated image sensors often include an image pixel array formed on a common semiconductor integrated circuit die with control circuitry such as analog control circuitry and digital control circuitry (sometimes referred to as a system-on-chip or SOC arrangement). In a frontside illuminated configuration, deep well isolation structures can be used to electrically isolate the analog circuitry from the control circuitry. However, in a backside illuminated configuration, the relatively thin semiconductor substrate can increase the capacitive coupling between deep well isolation structures as well as increasing the capacitive coupling between bond pads on the chip and the active substrate. If care is not taken, these increased capacitive couplings can respectively reduce the effectiveness of deep well isolation structures and can negatively impact performance of the chip in high speed applications.
It would therefore be desirable to be able to provide improved semiconductor circuits such as image sensors with improved noise isolation and high frequency performance.